An American college student who was recently released from North Korea has suffered severe brain damage, his doctors said Thursday, adding to growing calls in the US for a travel ban to the reclusive nation amid souring public sentiment and safety concerns.

Otto Warmbier (AP-Yonhap)

Otto Warmbier, 22, returned home to Ohio on Tuesday after being jailed in the communist state for more than 17 months following months of covert diplomacy led by Joseph Yun, a special representative for North Korea policy at the US State Department. But to the ire of his family and many US citizens, he was found to be in a coma and to have been in that state for some 15 months, triggering heated criticism over Pyongyang’s assumed mistreatment of the detainee.

“He (Warmbier) has spontaneous eye opening and blinking,” said Daniel Kanter, director of neurocritical care at the University of Cincinnati Health System, according to AP.

“However, he shows no signs of understanding language, responding to verbal commands or awareness of his surroundings. He has not spoken.”

Pyongyang reportedly told US officials that Warmbier contracted botulism and went into a coma after taking a sleeping pill. However, the family was skeptical over this claim.

AP also said that “doctors treating him in the US said they found no evidence of botulism, but did find severe brain damage consistent with losing oxygen to the brain.”

In a sign of consolation, President Donald Trump made a phone call to the student’s father. Fred Warmbier said at a news conference Thursday that Trump had said he was “sorry” and criticized his predecessor Barack Obama for his failure to obtain Otto Warmbier’s release earlier. Fred Warmbier had called the conversation “gracious” and “very candid.”

Otto Warmbier’s return has lent support to voices calling for a travel ban on North Korea, which has a long record of holding US nationals to use them as a bargaining chip. In Congress, a bipartisan bill was proposed in May by Republican Rep. Joe Wilson and Democratic Rep. Adam Schiff, which calls for Americans to be barred from touring the oppressive country and requiring them to obtain special permission for other types of visits.

“Tourist travel to North Korea does nothing but provide funds to a tyrannical regime -- that will in turn be used to develop weapons to threaten the United States and our allies,” Wilson said in a statement.

“We have been evaluating whether we should put some type of travel visa restriction to North Korea,” US Secretary of State Rex Tillerson told the House Foreign Affairs Committee on Wednesday. “We have not come to a final conclusion, but we are considering it.”

US media reports reflected public outrage and sentiment toward the North. The Wall Street Journal on Thursday argued for the ban, saying about 5,000 Western tourists take risks to go there each year and highlighting “dangers amplified by heightened tension” between Washington and Pyongyang.

“Tourism is one of the most visible ways in which North Korea retains ties to the outside world despite wide-ranging sanctions,” it said.

The Washington Post also condemned the North for its “horrendous mistreatment” of Warmbier and urged the US to step up sanctions on the Kim Jong-un regime.

“He was arrested, tried on spurious charges and evidently subjected to horrendous mistreatment by the North Korean authorities,” an editorial said Wednesday.

“This was outrageous behavior even by the standards of one of the world’s most vicious and isolated regimes. It should not go unpunished.”